Sirens wailed as fire trucks, ambulances, paramedics and police rushed to the scene.
Hundreds of orange-clad, helmet-wearing workers were corralled into safe areas under the direction of safety officers.
Firefighters wearing breathing apparatus and carrying heavy-looking rescue equipment rushed into the entrances to Te Waihorotiu Station and disappeared underground.
Onlookers watched nervously from behind safety barriers, and waited.
![Police and ambulance responders during the exercise. Photo / Jason Oxenham](https://www.nzherald.co.nz/resizer/v2/T2K2KFLUWJALNF5INMBCTAP4F4.jpg?auth=6773bd59d3e50df293c20eb14d6f0efd1e2754c7c340bec6e7579b5b91955fff&width=16&height=11&quality=70&smart=true)